Cannot enable Administrator account

Here's a wierd one...

On starting up my PC today (Win 7 Home Premium) I have lost all Admin
accounts.

I am a Standard User but NOT an Admin any more.

If I try to enable Admin I get a UAC box with a GREYED OUT YES button (I
can only click NO).

This means I cannot:

run anything as Admin
enable admin account
create new admin account
turn off UAC

Anything that prompts a AUC box has NO WAY to click YES/OK

Unser ControlPanel/User Accounts there is only one Standard User account
and NO Admin accounts.
I of course cannot create an admin account beacause of UAC.
I cannot disable UAC bacause of UAC.
cmd - "net user administrator /active:yes" does not work (I need to be
an Admin for this!).


HELP!!


TIA

Guy